1. Field of the Invention
The present invention relates to a micro-switching element fabrication method that utilizes MEMS technology. The present invention also relates to a micro-switching element produced by such a method.
2. Description of the Related Art
In the technical field of wireless communications devices such as mobile telephones, an increasing number of parts are required for providing high-quality products. At the same time, the product should be small enough so that the user can carry it easily. To make such a compact wireless communications device, high-frequency circuits or RF circuits should be made small. To meet this requirement, MEMS technology is adopted for making infinitesimal components that constitute a required circuit.
An example of such infinitesimal components is an MEMS switch. Typically, an MEMS switch includes a pair of contact electrodes and a pair of driving electrodes. The contact electrodes are opened and closed mechanically for implementing the switching function. The driving electrodes are provided for realizing the switching operation of the contact electrodes by electrostatic force. For high-frequency switching operation (e.g., on GHz order), an MEMS switch is more advantageous than a conventional PIN diode switch or MESFET switch, since the MEMS switch can provide better electrical insulation in the open circuit state and suffer lower insertion loss. Conventional MEMS switches are disclosed in JP-A-09-173000 and JP-A-2000-188050, for example.
FIGS. 20 and 21 show a conventional MEMS micro-switching element X3. FIG. 20 is a plan view showing the principal portions of the switching element X3, while FIG. 21 is a sectional view taken along lines XXI-XXI in FIG. 20. The switching element X3 includes a substrate 301, a pair of contact electrodes 302, two driving electrodes 303, a movable member 304 and reinforcing plating layers 305. The contact electrodes 302 are formed on the substrate 301 and spaced from each other. The two driving electrodes 303 are formed on the substrate 301 in a symmetrical manner with respect to the contact electrodes 302. The movable member 304 extends over the contact electrodes 302 and the driving electrodes 303 on the substrate 301. The movable member 304 as a whole may be made of an electroconductive material. As shown in FIG. 21, the movable member 304 is formed with a contact electrode portion 304a and two driving electrode portions 304b. The contact electrode portion 304a is arranged to face the inner ends of the respective contact electrodes 302 (see also FIG. 20), while each driving electrode portion 304b is arranged to face a corresponding one of the driving electrodes 303. The plating layer 305 is provided for reinforcing the connection between the movable member 304 and the substrate 301. Though not shown in the figures, a wiring pattern is formed on the substrate 301 to be connected to the contact electrodes 302, the driving electrodes 303 or the movable member 304. In the switching element X3, the movable member 304 is resilient and can be deformed downward when electrostatic attraction is generated between the driving electrodes 303 and the driving electrode portions 304b. The movable member 304 is deformed until the contact electrode portions 304a come into contact with the contact electrodes 302.
FIGS. 22A˜22D and FIGS. 23A˜23D show some steps of a process for making the above-described switching element X3. First, as shown in FIG. 22A, driving electrodes 303 are formed on a substrate 301 by patterning. Then, as shown in FIG. 22B, contact electrodes 302 are formed between the driving electrodes 303 by pattering. As shown in FIG. 22C, a sacrifice layer 306 is formed on the substrate 301 by depositing an appropriate material. As shown in FIG. 22D, the sacrifice layer 306 is patterned into a predetermined configuration by etching, for example. Then, as shown in FIG. 23A, a layer 304′ is formed to cover the sacrifice layer 306 and the substrate 301. As shown in FIG. 23B, the layer 304′ is formed into a movable member 304 by patterning. As shown in FIG. 23C, a reinforcing plating layer 305 is formed on each end of the movable member 304. Then, as shown in FIG. 23D, the sacrifice layer 306 is etched away to provide a space between the substrate 301 and the movable member 304.
In the process for making the micro-switching element X3, the patterning of the sacrifice layer 306 need be performed, as described above with reference to FIG. 22D. In addition, as described above with reference to FIG. 23C, the reinforcing plating layers 305 need be formed on the respective ends of the movable member 304. Unfavorably, the sacrifice layer patterning step and the reinforcing layer forming step lower the yield of the switching elements X3.
FIGS. 24 and 25 show another conventional MEMS micro-switching element-switching element X4. FIG. 24 is a plan view showing the principal portions of the switching element X4, while FIG. 25 is a sectional view taken along lines XXV-XXV in FIG. 24. The switching element X4 includes a substrate 401, a pair of contact electrodes 402, two driving electrodes 403, a pair of supporting members 404 and a movable beam 405. The paired contact electrodes 402 are formed on the substrate 401 and spaced from each other. The two driving electrodes 403 are formed on the substrate 401 in a symmetrical manner with respect to the contact electrodes 402. The two supporting members 404 are mounted on the substrate 401 in a symmetrical manner with respect to these electrodes. The movable beam 405 bridges between the supporting members 404, to extend over the contact electrodes 402 and the driving electrodes 403. The supporting members 404 are made of an insulating material, while the movable beam 405 as a whole may be made of an electroconductive material. The movable beam 405 is formed with a contact electrode portion 405a and two driving electrode portions 405b. The contact electrode portion 405a is arranged to face the inner ends of the respective contact electrodes 402, while each driving electrode portion 405b is arranged to face a corresponding one of the driving electrodes 403. Though not shown in the figures, a wiring pattern is formed on the substrate 401 to be connected to the contact electrodes 402, the driving electrodes 403 and the movable beam 405. In the micro-switching element X4, the movable beam 405 is resilient and can be deformed downward when an electrostatic force is generated between the driving electrodes 403 and the driving electrode portions 405b, so that the contact electrode portions 405a come into contact with the contact electrodes 402.
FIGS. 26A-26D and FIGS. 27A-27D show some steps of a process for making the above-described switching element X4. First, as shown in FIG. 26A, contact electrodes 402 and driving electrodes 403 are formed on a substrate 401 by patterning. Then, as shown in FIG. 26B, a pair of supporting members 404 is formed by depositing an appropriate material on the substrate 401 and patterning the resultant material layer. As shown in FIG. 26C, a layer 406′ is formed to cover the contact electrodes 402, the driving electrodes 403 and the supporting members 404 by depositing an appropriate material on the substrate 401. As shown in FIG. 26D, the surface of the layer 406′ is ground until the top surfaces of the respective supporting members 404 are exposed. Thus, a sacrifice layer 406 is obtained, which has the same thickness as the supporting members 404. Then, as shown in FIG. 27A, the sacrifice layer 406 is subjected to etching to be provided with a predetermined surface configuration. As shown in FIG. 27B, a conductive layer 405′ is formed on the sacrifice layer 406. As shown in FIG. 27C, the layer 405′ is patterned into a movable beam 405. Then, as shown in FIG. 27D, the sacrifice layer 406 is etched away to provide a space between the substrate 401 and the movable beam 405.
In the process for making the switching element X4, the paired supporting members 404 need be formed on the substrate 401 by patterning, as described above with reference to FIG. 26B. In addition, as described above with reference to FIG. 26D, the material layer 406′ need be ground to provide a sacrifice layer 406 having the predetermined thickness. Unfavorably, these steps lower the yield of the switching elements X4.